Abstract

Multielemental microanalysis of commercially available aluminum alloys has been performed in air by laser-induced breakdown spectroscopy (LIBS) by use of UV laser pulses with energies below 10 µJ. It is shown that the LIBS technique is capable of detecting the elemental composition of particles less than 10 µm in size, such as precipitates in an aluminum alloy matrix, by using single laser shots. Chemical mapping with a lateral resolution of ∼10 µm of the distribution of precipitates in the surface plane of a sample was also carried out. Two main types of precipitate, namely, Mn-Fe-Cu (type I) and Mg-Cu (type II), were unambiguously distinguished in our LIBS experiments, in good agreement with x-ray microanalysis measurements. The relative standard deviations of emission of the main minor constituent elements (Cu, Mg, Mn) of the aluminum 2024 alloy range from 33% to 39% when laser shots on the precipitates are included in the analysis but decrease to a range from 5.3% to 7.4% when laser shots are taken only on the matrix material, excluding the precipitates.

Figures (8)

SEM of an Al 2024 alloy surface taken in backscattered electron mode. The bright areas correspond to the precipitates with higher concentrations of high-Z elements such as Cu, Mn, and Fe compared with the Al matrix (dark areas).

SEMs of an Al 2024 alloy surface taken in both backscattered electron (a)–(c) and secondary-electron (d) modes with craters produced by single UV laser shots of pulse energies of ∼7 µJ on a matrix (M1 and M2) and on selected precipitates (P1 and P2).

Distribution of line intensities of the corresponding constituent elements of the Al 2024 alloy sample over 98 consecutive laser shots. Horizontal dashed lines, corresponding 3σ deviations from the average matrix values. Multiplication of a shot number by 10 gives the corresponding lateral distance across the sample’s surface in micrometers.

Tables (2)

Table 2 Comparison of the RSDs of the X-Ray Microanalysis Measured Concentrations of Main Constituent Elements in an Al 2024 Alloy Sample and the RSD of the Corresponding Line Intensities Measured by LIBS

a Values represent the averages of 16 measurements of the matrix material and 3 measurements of precipitates; standard deviations for the measurements are also given. The element Cr was not detectable in any of these samples.

Table 2

Comparison of the RSDs of the X-Ray Microanalysis Measured Concentrations of Main Constituent Elements in an Al 2024 Alloy Sample and the RSD of the Corresponding Line Intensities Measured by LIBS

a Values represent the averages of 16 measurements of the matrix material and 3 measurements of precipitates; standard deviations for the measurements are also given. The element Cr was not detectable in any of these samples.

Table 2

Comparison of the RSDs of the X-Ray Microanalysis Measured Concentrations of Main Constituent Elements in an Al 2024 Alloy Sample and the RSD of the Corresponding Line Intensities Measured by LIBS